Anti-oxidant and Anti-Inflammatory Cyclic Diarylheptanoids from Alnus japonica Stem Bark.

A new cyclic diarylheptanoid namely alnuheptanoid B (3), along with four known cyclic diarylheptanoids: myricanone (1), (+)-S-myricanol (2), myricanone 5-O- -D-glucopyranoside (4), and (+)-S-myricanol 5-O- -D-glucopyranoside (5) were isolated from the EtOAc fraction of Alnus japonica Steud (family: Betulaceae) stem bark. Their structures were established by different spectroscopic analyses, as well as optical rotation measurement. Compounds 1, 2, 4, and 5 are isolated for the first time from A. japonica. The antioxidant and anti-inflammatory activities of compounds (1-5) were assessed using DPPH assay and carrageenin induced rat paw edema model, respectively. They displayed significant antioxidant activity in relation to propyl gallate (standard antioxidant) at concentration 50 µM. Compound 2 demonstrated anti-inflammatory effect at a dose 10 mg/kg compared with indomethacin (positive control).


Plant material
The plant sample was obtained from the Heinrich-Heine University`s botanical garden (Düsseldorf, Germany) in March 2005. The plant was taxonomically authenticated and identified by Peter Westhoff, Prof. of Plants Molecular Biology and Development (Heinrich-Heine University, Germany). A specimen (Registration code AJB-2005) was kept at the Faculty of Pharmacy, Department of Pharmacognosy, Al-Azhar University, Egypt.
Carrageenin-induced rat paw edema method The anti-inflammatory activity was evaluated on adult male albino rats (120-150 g b. wt.) using the same procedures as previously described (23, 25 ,26).

Statistical analysis
All data were expressed as mean ± standard error of mean using the student t test. ANOVA (one-way analysis of variance) was used for evaluation of statistical significance. The values were considered to be significantly different when P < 0.01.
Compounds 1-5 were evaluated for their antiinflammatory effects using carrageenin induced paw edema model. Compound 2 showed the highest activity comparable to indomethacin (10 mg/kg) (Table 4). Also, 1, 3, 4, and 5 showed potent activity at dose 10 mg/kg after 4 h. The phenolic compounds are known to inhibit prostaglandins synthesis enzymes, more specifically the endoperoxide (26). It was reported that, prostaglandin like substances are released during the second phase of carrageenin induced edema (34, 35). So, the anti-inflammatory effects of the tested compounds may be due to inhibition of prostaglandin like substances.
The observed activity of these compounds might be through the inhibition of the inflammatory prostanoids (36,37). In this work, we can make a conclusion on the SAR of the tested cyclic diarylheptanoids. It was observed that, the phenolic hydroxyl groups are responsible for anti-inflammatory activity as in 1 and 2 (36, 37). Glucosidation of phenolic OH group leads to reduce the activity as in 3-5. Secondary alcoholic hydroxyl group in aliphatic chain might increase the activity as in 1 and 5 in comparison to the other compounds.

Conclusions
A new cyclic diarylheptanoid and four known compounds were isolated from A. japonica for the first time. Their chemical structures were established by different spectroscopic analyses.